Some of the bits I found most interesting:
From Part I:
This brings us to the most fundamental fact of rural life in the pre-modern world: the grain is harvested once a year, but the family eats every day. Of course that means the grain must be stored and only slowly consumed over the entire year (with some left over to be used as seed-grain in the following planting). That creates the first cycle in agricultural life: after the harvest, food is generally plentiful and prices for it are low (we’ll deal with the impact this has on trade and markets a little later). As the year goes on, food becomes scarcer and the prices for it rise as each family ‘eats down’ their stockpile.
Also from part I, how farmers focused not on maximising the yield from a crop but on minimising risk of a really bad harvest:
Most modern folks think in terms of profit maximization; we take for granted that we will still be alive tomorrow and instead ask how we can maximize how much money we have then (this is, admittedly, a lot less true for the least fortunate among us). We thus tend to favor efficient systems, even if they are vulnerable. From this perspective, ancient farmers – as we’ll see – look very silly, but this is a trap, albeit one that even some very august ancient scholars have fallen into. [...] These small subsistence farmers generally seek to minimize risk, rather than maximize profits. After all, improving yields by 5% doesn’t mean much if everyone starves to death in the third year because of a tail-risk that wasn’t mitigated. [...] So as we’ll see, these farmers generally sacrifice efficiency for greater margins of safety, every time.
Part III was the most interesting to me, as I learnt the mechanics of turning a field of wheat into bread. Here's a good bit on why wheat is usually turned into flour instead of being consumed whole grain like rice:
Raw unmilled barley and wheat can be made edible by roasting, or better yet turned in to porridge by boiling the grains in equal parts grain and water for roughly an hour or so. [...] But turning grain into bread has nutritional advantages, breaking down some of the harder to digest plant compounds and cell-walls, thus allowing the human body to derive more nutrition from the bread itself than it would from the grains.
From part IV; how much cheaper water transport was compared to land transport. I didn't expect sea transport to be 20x cheaper:
Using the figures from the Price Edict of Diocletian, we tend to estimate that river transport was five times cheaper than land transport, and sea-transport was twenty times cheaper than land transport. So while the transport of bulk goods like grain on land was limited to fairly small amounts moving over short distances – say from the farm to the nearest town or port – grain could be moved long distances en masse by sea.